The goal of this project is to produce high-density electrode arrays that can be inserted into the cochleae of deaf subjects to improve their contact with the auditory world. The electrode arrays that are used in today's cochlear implants have, at most, 24 electrodes that can be stimulated only one at a time. We have developed a 72-electrode array whose contacts can be excited in groups of 3-36. The high density of electrodes and an active means to approximate them to surviving auditory neurons makes it possible to excite several independent groups of neurons simultaneously. The result should be easier recognition of sound by the wearers of the new devices. In 1998 we perfected and patented the means to bring the electrodes near the auditory neurons. We use an electrically activated shape memory core of Nitinol(r) wire, which is an alloy of nickel and titanium. The core is annealed in a mold that has the shape of the central wall of the scala tympani (the location of t he auditory nerve cells). After it is cooled, the core can be straightened. By driving electric current through the wire, the wire self-heats to 40!C and assumes the shape of the scala tympani as the surrounding array of wires is inserted gently into the cochlea. We have now demonstrated the feasibility of the active core and of multi-layered arrays, but we have not yet implanted the arrays in monkeys because we measured pinholes in the insulation and discovered some delamination of the arrays. We are working on both problems at this time and expect to test the arrays in monkeys this year. FUNDING NIH/NIDCD grant DC02424. Boogaard, J., Spelman, F., and Clopton, B. Development of high density electrode arrays. BioEngineering, Building the Future of Biology and Medicine, BECON, NIH Symposium, February 27-28, p. 40, 1998 (abstract). Spelman, F.A., Clopton, B.M., Voie, A., Jolly, C.N., Huynh, K., Boogaard, J., and Swanson, J.W. Cochlear implant with shape memory material and method for implanting the same. U.S. Patent 5,800,500, September 1, 1998.